Method for accomplishing a high driving force at a combustion gas driven impact device and an impact device for carrying out of said method

ABSTRACT

A method and a device for obtaining high energy impacts mainly for demolishing purposes. In a piston-cylinder device, the cylinder is charged with pressurized combustible gas at both sides of the piston and a rearwardly directed compression stroke is initiated by ignition of the gas volume at the forward end of the piston. At a certain pressure, the compressed gas volume within the rear end of the cylinder is ignited and a forwardly directed working stroke is initiated. The device comprises a gas supply system and two ignition systems, one of which is manually controlled for the compression stroke initiating and the other is a pressure sensitive automatic system for the working stroke initiating. The impact device also comprises a retarding device by which kinetic energy is absorbed from the piston unit at the end of the working strokes.

United States Patent .1191 1111 3,827,410

Erma et al. Aug. 6, R974 METHOD FOR ACCOMPLISHING A HIGH 2,273,0952/1942 Fitch 173/134 DRIVING FORCE AT A COMBUSTION GAS if? 1 DRIVENIMPACT DEVICE AND AN IMPACT 3:l6l:l84 12/1964 Koftan IIIH III 1 23/46 HDEVICE FOR CARRYING OUT OF SAID 3,253,399 5/1966 Bakhtar et al.. 60/26.1

A METHQQ W V w w 3,320,740 5/l967 Hamkins 60/26.]

[75] Inventors: Eero Amem Erma, Klinwn; 3,468,222 9/1969 Cordesetal173/134 Stig Berti! Arthur Fredin,

I-Ia d K l (1 m Li dh, Primary Examiner-Wendell E. Burns Sollentuna; LeoAnders Timgren, Saltsjo-Boo, all of Sweden [57] ABSTRACT [73] Asslgnee:Atlas Copco Aktlebolag Nacka A method and a device for obtaining highenergy imma is 9 V 3 pacts mainly for demolishing purposes. In a plston-[22] Filed: Dec. 7, 1972 cylinder device, the cylinder is charged withpressurized combustible gas at both sides of the piston and a rearwardlydirected compression stroke is initiated by ignition of the gas volumeat the forward end of the [21] Appl. No.: 313,130

[ oreign Application Priority Da a piston. At a certain pressure, thecompressed gas v01- Dec. 13, 1971 Sweden 15926/71 me within the rear n othe cylinder is ignited and a forwardly directed working stroke isinitiated. The

[52] U.S. Cl. 123/46 R, 173/134 device Comprises a gas pp y system andtwo g n [51] Int. Cl F02b 71/00 systems, one of hic is anuallycontrolled for the [58] Field of Search 123/46 R, 46 5C, 46 A,compression stroke initiating and the other is a pres- 123 4 H; 173 134;0/2 1 sure sensitive automatic system for the working stroke initiating.The impact device also comprises a retard- [56] R f r Cit d ing deviceby which kinetic energy is absorbed from UNITED STATES PATENTS thepiston unit at the end of the working strokes.

2.203730 7/1940 Pfeiffer 173/134 8 Claims, 3 Drawing Figures i 6 IO I918 l7 2O PAIENTEDMIB 61914 3.827.410

SHEET 2 BF 3 Fig. 2

METHOD FOR ACCOMPLISHING A HIGH DRIVING FORCE AT A COMBUSTION GAS DRIVENIMPACT DEVICE AND AN IMPACT DEVICE FOR CARRYING OUT OF SAID METHODrational would be to demolish the constructions by applying a limitednumber of high power strokes thereon. However, there has not been anyimpact devices available which develop sufficient high impact energy andwhich are suitable for practical use.

Another object of the invention is to obtain impact strokes the energyof which are large enough to perform a complete cold forging operationin one stroke.

These problems are solved by the method and the impact device as theyare stated in the claims.

The invention is herebelow described with reference to the drawings onwhich FIG. 1 shows partly in section a longitudinal section through animpact device adapted to the method according to the invention.

FIG. 2 shows schematically an impact device according to the inventionand the pneumatic and electric control circuits connected thereto.

FIG. 3 shows, in larger scale, a longitudinal section through ahydraulic retarding device which constitutes a part of the impact deviceaccording to FIG. 1.

The impact device shown in FIG. 1 comprises a main frame 1, a cylinderhousing 2 and a piston unit 3. The latter comprises a piston 4, a pistonrod 5 and a tool 6 connected to the forward end of the piston rod 5. Thecylinder housing 2 has a rear combustion chamber 7 and a forwardcombustion chamber 8 which both are provided with inlet openings 9 and10, respectively, which are intended for supplying the combustionchambers with combustible gas. The combustion chambers 7 and 8 are alsoprovided with spark plugs 11 and 12, respectively. To the inlet openings9 and 10, there are connected mixture nozzles 14 and 15. The twocombustion chambers 7 and 8 have in common an outlet opening 16 fordraining of the cylinder housing 2. Moreover, the main frame 1 isprovided with two latch dogs 17 which are pivotable between a restposition and a position in which they are in positive engagement with aflange 18 on the tool 6. The latch dogs 17 are pivoted toward theirengagement positions by means of pneumatic cylinders 19 and to theirrest positions by means of tension springs 20.

Furthermore, the impact device is provide with a hydraulic retardingdevice 22, consisting of an annular piston 23 and a cylinder chamber 24.The piston 23 is freely movable relative to the piston rod 5 andarranged so as to be struck by the piston 4 at the end of the workingstroke. The cylinder chamber 24 is connected to a pressure accumulator25 and a pneumatically driven hydraulic pump 27. The latter is connectedto a tank 21.

In FIG. 2 there is shown ignition and combustible gas supply systems foran impact device according to the invention. Petrol enriched compressedair may very well be used as combustible gas. The pressure air supply iscontrolled by an electrically operated valve 28 and petrol is suppliedthrough a valve 29 of the same type. The valves 28 and 29 are bothprovided with electromagnetic control means 30, 31 and 32, 33. Thesecontrol means are connected to a current source via a common switch 34.The valve 28 is supplied with compressed air through a conduit 35 andthe valve 29 is supplied with petrol through a conduit 36. The petrolpressure is preferably a bit higher than that of the air. Thedown-stream end of the air valve 28 is connected to the mixture nozzles14 and 15 through conduits 37 and 38, respectively, while thedown-stream end of the petrol valve is connected to the mixture nozzlesthrough conduits 39 and 40.

The control system of the impact device comprises a pressure switch 41which is connected to the combustion chamber 7. The electric circuitcomprising the control means of the valves 28, 29 is arranged to beclosed by the switch 41 as a predetermined pressure is obtained in thecylinder housing 2. Thereby, petrol and pressure air supply to thecylinder housing is interrupted. The pressure switch 41 is connected tothe current source through a line 42 and to the control means 33 and 30by conduits 43 and 44.

Moreover, the impact device is provided with an ignition device 45 forsupplying high tension current to the spark plug 11 of the rearcombustion chamber 7. The ignition device 45 is in turn connected to thecurrent source via a line 46 and a switch 47. The switch 47 is actuatedby a heel 48 on the tool 6.

The control system comprises an ignition device 49 for supplying hightension current to the spark plug 12 of the forward combustion chamber8. This ignition device 49 is connected to the current source throughline 50 and a pressure switch 51. The latter is connectible to thepressure air source by means of the pressure air valve 28.

Finally, the impact device is provided with a control system foractuating the latch dogs 17. They are pivotable toward their engagementposition by means of the pneumatic cylinders 19. These are pressurizedby the pressure air source through conduits 52, 53 and an electricallyshiftable valve 54. The valve 54 is provided with electric manoeuvermeans 55 which are supplied with electric current from the currentsource through a line 56 and a switch 57. The valve 54 is shifted in onedirection by means of the manoeuver means 55 and in the oppositedirection by a spring 58.

The electric control system is connected to earth through the machineand because of that only one of its poles is shown in FIG. 2.

The cylinder chamber 24 of the hydraulic retarding device 22 comprises anumber of outlet openings 60, 61, 62 and 63 which are disposed atdifferent levels. During its forward directed movement, the piston 23successively register with one after the other of these holes. As all ofthe openings -63 communicate with the conduit 26, the total outlet areaof the cylinder chamber 24 is restricted as the piston covers them,whereby a retarding force is obtained.

The operation order of the impact device shown in the drawings is thefollowing,

Before the working cycle is started, the piston unit 3 is fixed in astart position (see FIGS. 1 and 2). The piston unit 3 is locked in thisposition in that the switch 57 is shifted so that the manoeuver means 55is supplied with current and shifts the valve 54 against the biasingforce of the spring 58. Compressed air is now able to pass through thevalve 54 and activate the cylinders 19 so that they, against the biasingforce of the springs 20, pivot the latch dogs 17 toward their activepositions in which they cooperates with the flange 18 of the tool 6. Theswitch 57, which is spring biased to its non-active position, may nowbreak the electric circuit. Despite that, the latch dogs 17 are stillkept in their locking positions because of the fact that the piston unit3 rests upon them with all its weight. As the piston unit 3 has beenfixed in its start position, the switch 34 is shifted so that theactivating means 31 and 32 of the valves 28, 29 are fed with electriccurrent. Then the valves 28, 29 are shifted so that pressure air andpetrol are supplied to the mixture nozzles 14, and through the conduits37, 38 and 39, 40.

Because of the fact that the piston 4 covers the outlet opening 16 inits start position, a charge pressure is built up in both of thecombustion chambers 7 and 8 of the cylinder housing 2. When fullpressure is obtained, the pressure switch 41 is shifted so that theactivating means and 33 of the valves 28, 29 are supplied with electriccurrent. The valves 28 and 29 are then shifted so that the air-petrolsupply to the cylinder housing 2 is interrupted. On the contrary, thevalve 28 directs pressure air to the pressure switch 51 which in turnconnects the ignition device 49 to the electric current source. Theignition device 49 accomplishes a spark upon the spark plug 12 so thatthe petrol enriched pressure air in the forward combustion chamber 8 isignited.

Due to the combustion within the forward combustion chamber 8, thepiston unit 3 is accelerated into a rearwardly directed compressionstroke. Immediately, the tension springs 20 return the latch dogs 17 totheir rest positions. The combustible gas, enclosed in the rearcombustion chamber 7, is now compressed. When the piston 4 gets close toits rear end position the outlet opening 16 is uncovered so that theforward combustion chamber 8 is drained to the atmosphere and releasedfrom pressure. As the piston 4 has reached its rear end position, theswitch 47 is acted upon by the heel 48 of the tool 6, whereby theignition device 43 is supplied with electric current. This, in turn,results in a spark upon the spark plug 11 and an ignition of thesuper-compressed gas in the rear combustion chamber Owing to the factthat the rear combustion chamber 7 has been over-charged withpetrol-enriched pressure air, the driving force acting upon the piston 4during the succeeding working stroke is very high. The piston unit 3 isaccelerated forwards in order to perform a working stroke. As the latchdogs 17 are released from the piston unit weight they are automaticallypivoted to the rest positions by means of the tension springs 20. Then,they give free passage for the tool. When getting close to its forwardend position, the piston 4 uncovers the outlet opening 16 and the rearcombustion chamber-7 is released from pressure.

After having performed the intended work, but before reaching itsforward end position, the piston 4 strikes the piston 23. As thepressure accumulator 25 has been pre-charged to a pressure exceeding themaximum driving pressure obtained in the forward combustion chamber 8,the piston 23 is kept in its rear position even during the compressionstroke. The pressure accumulator 25 may very well be charged withnitrogen gas of a pressure of about 50 atmospheres. As the retard piston23 is struck by the piston 4 and thereby driven forwardly, hydraulicfluid is pressed out through the openings 6063 and further on throughthe conduit 26 to the pressure accumulator 25. The nitrogen gas is thenfurther compressed. During its forward movement, the piston 23successively register with the outlet openings 60-63, whereby the totaloutlet area of the cylinder chamber 24 is diminished. This causesrestriction of the hydraulic fluid flow from the chamber 24, whereby thekinetic energy of the piston unit 3 is ab sorbed. As the piston unit 3has been stopped, a return stroke is immediately started. This isaccomplished by action of the pressure accumulator 25 which presseshydraulic fluid back into the cylinder chamber 24.

In order to keep up the hydraulic fluid level in the chamber 24, as acompensation for leakage, the pump 27 works continuously. The pump 27 isactuated by pulsating pressure air and is provided with two check valvesfor accomplishing the intended hydraulic fluid flow from the tank 21 tothe retarding device 22.

Before every succeeding working cycle, the piston unit 3 has to belifted up to and locked in its start position. This lifting operationcould very well be carried out by supplying pressure air to the forwardcombustion chamber 8. This pressure is released before combustible gasis introduced. This operation is performed by a pneumatic circuit notshown in the drawings.

Owing to the fact that the impact device is overcharged withpetrol-enriched pressure air and that the combustible gas is still morecompressed during the compression stroke, the impact device according tothe invention is able to develope a very high energy at each stroke. Byusing a high combustion pressure for driving the piston unit, it ispossible to keep down the over-all dimensions of the impact device andmake the latter suitable for practical use, for instance for mounting ona tractor.

At an impact device according to the invention, the drive pressurewithin the rear combustion chamber is of a magnitude of aboutatmospheres at a piston unit weight of about 400 kilograms. The obtainedimpact energy per stroke is about 5,000 kpm.

The invention is not limited to the shown and described embodiments butcan be freely varied within the scope of the claims.

What we claim is:

1. Method for accomplishing a large driving force at a combustion gasdriven impact device comprising a cylinder housing and a piston unit,reciprocable in said cylinder housing, said piston unit comprising apiston and a piston rod, characterized in that, before every workingstroke, the piston unit is fixed in a start position in which the pistonis situated at distances from the ends of the cylinder housing, that thecylinder housing is charged with compressed, combustible gas at bothends of the piston, that a rearwardly directed compression stroke isinitiated by ignition of the gas volume in front of the piston, that thefront part of the cylinder housing is released from pressure at the endof the compression stroke and that a forwardly directed working strokeis initiated by ignition of the compressed combustible gas in the rearpart of the cylinder housing.

2. Method according to claim 1, characterized in that the compressionstroke is initiated automatically when a predetermined charge pressureis reached within the cylinder housing and that the working stroke isinitiated when the piston has reached a predetermined position relativeto the cylinder housing.

3. Method according to claim 1, characterized in that, before everyworking cycle, the piston is fixed in its start position by mechanicalmeans.

4. Method according to any of the claims 1, characterized in that thecylinder housing is charged with a mixture of petrol and compressed airat the beginning of the working cycle.

5. Impact device comprising a cylinder housing which is provided withcombustion chambers at its opposite ends, a piston unit comprising apiston and a piston rod reciprocably guided within said cylinderhousing, characterized in that the cylinder housing is provided withinlet openings for simultaneous supply of combustible gas to both of thecombustion chambers, that means are arranged to fix the piston in astart position at distances from the ends of the cylinder; 21 firstignition system for ignition of combustible gas within the combustionchamber in front of the piston in the working stroke direction of thelatter, and a second ignition system for ignition of combustible gaswithin the combustion chamber situated behind the piston.

6. Impact device according to claim 5, characterized in that thecombustible gas is constituted by a mixture of compressed air andpetrol.

7. Impact device according to any of the claims 5, characterized by ahydraulic retarding device which is arranged to absorb kinetic energyfrom the piston unit at the end of the working stroke.

8. Impact device according to claim 5, characterized in that means areprovided to activate said first ignition system automatically at apredetermined charge pressure of the supplied combustible gas and thatmeans are provided to activate said second ignition system automaticallyat a predetermined position of the piston.

1. Method for accomplishing a large driving force at a combustion gasdriven impact device comprising a cylinder housing and a piston unit,reciprocable in said cylinder housing, said piston unit comprising apiston and a piston rod, characterized in that, before every workingstroke, the piston unit is fixed in a start position in which the pistonis situated at distances from the ends of the cylinder housing, that thecylinder housing is charged with compressed, combustible gas at bothends of the piston, that a rearwardly directed compression stroke isinitiated by ignition of the gas volume in front of the piston, that thefront part of the cylinder housing is released from pressure at the endof the compression stroke and that a forwardly directed working strokeis initiated by ignition of the compressed combustible gas in the rearpart of the cylinder housing.
 2. Method according to claim 1,characterized in that the compression stroke is initiated automaticallywhen a predetermined charge pressure is reached within the cylinderhousing and that the working stroke is initiated when the piston hasreached a predetermined position relative to the cylinder housing. 3.Method according to claim 1, characterized in that, before every workingcycle, the piston is fixed in its start position by mechanical means. 4.Method according to any of the claims 1, characterized in that thecylinder housing is charged with a mixture of petrol and compressed airat the beginning of the working cycle.
 5. Impact device comprising acylinder housing which is provided with combustion chambers at itsopposite ends, a piston unit comprising a piston and a piston rodreciprocably guided within said cylinder housing, characterized in thatthe cylinder housing is provided with inlet openings for simultaneoussupply of combustible gas to both of the combustion chambers, that meansare arranged to fix the piston in a start position at distances from theends of the cylinder; a first ignition system for ignition ofcombustible gas within the combustion chamber in front of the piston inthe working stroke direction of the latter, and a second ignition systemfor ignition of combustible gas within the combustion chamber situatedbehind the piston.
 6. Impact device according to claim 5, characterizedin that the combustible gas is constituted by a mixture of compressedair and petrol.
 7. Impact device according to any of the claims 5,characterized by a hydraulic retarding device which is arranged toabsorb kinetic energy from the piston unit at the end of the workingstroke.
 8. Impact device according to claim 5, characterized in thatmeans are provided to activate said first ignition system automaticallyat a predetermined charge pressure of the supplied combustible gas andthat means are provided to activate said second ignition systemautomatically at a predetermined position of the piston.